The invention relates to a lower thread tension adjusting device used in combination with a sewing machine.
When a fabric is sewn with a sewing machine, it is generally necessary to properly adjust the upper and lower thread tension in dependence upon a kind or thickness of the fabric as well as the stitching types. For this purpose, hitherto, a bobbin carrier or bobbin case is provided with an abutment and a leaf spring to give a tension to a lower thread carried by the bobbin carrier or bobbin case. More particularly, by manipulation of an adjusting screw the pressure of the leaf spring against the abutment is adjusted to thereby adjust the tension of the thread extending between the abutment and the leaf spring. The operation of such a conventional adjustment of lower thread tension is, however, very troublesome and time-consuming. Moreover, it has been impossible to adjust the tension during the stitching operation. Further, the adjustment has to be carried out by guesswork, which often requires readjustment.